ITS335 Web Security Browsing Applications Web Security HTTPS Certificates Summary ITS335: IT Security Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 2 February 2014 its335y13s2l09, Steve/Courses/2013/s2/its335/lectures/websecurity.tex, r3104 1/31
ITS335 Contents Web Security Browsing Web Browsing Applications HTTPS Certificates Web Applications Summary Confidential Web Communications with HTTPS Digital Certificates Summary 2/31
ITS335 Web Browsing with HTTP Web Security Browsing Applications HTTPS Certificates Summary 3/31
ITS335 Web Browsing with HTTP Web Security Browsing Applications HTTPS Certificates Summary 4/31
ITS335 Web Access with Hypertext Transfer Protocol Web Security ◮ HTTP is a request/response protocol for web browsing Browsing ◮ HTTP is stateless; no dependence between a request Applications and previous request HTTPS ◮ User Agent (client) sends HTTP Request message Certificates Summary ◮ Server responds with HTTP Response message ◮ Default server port number: 80 ◮ Generic HTTP message format: Start line Optional header lines <empty line> Optional message body ◮ Start line differs for request and response ◮ Header format: field-name: value 5/31
ITS335 HTTP Example Web Security Browsing Applications HTTPS Certificates Summary 6/31
ITS335 HTTP Request Messages Web Security ◮ Start line: Method URL Version Browsing ◮ Methods: Applications ◮ GET: retrieve the resource at the specific URL HTTPS ◮ HEAD: same as GET, except do not return message Certificates body (only header) Summary ◮ OPTIONS: retrieve options available for resource or server ◮ POST: asks server to accept and process the attached data at the resource ◮ . . . ◮ Version: version of HTTP, e.g. HTTP/1.0, HTTP/1.1 7/31
ITS335 HTTP Response Messages Web Security ◮ Start line: Version StatusCode StatusReason Browsing ◮ Status Codes and Reasons: Applications ◮ 100: Continue (the client should continue with its HTTPS request) Certificates ◮ 200: OK (the request succeeded) Summary ◮ 301: Moved Permanently (the requested resource has a new URL) ◮ 304: Not Modified (resource hasnt changed since last request, client should use cached copy) ◮ 401: Unauthorized (request must include user authentication) ◮ 403: Forbidden (request was understood, but server refuses to process it) ◮ 404: Not Found (server cannot find resource at requested URL) ◮ 503: Service Unavailable (server currently unable to handle request, e.g. server is too busy) 8/31
ITS335 HTTP Headers Web Security ◮ Date: data and time of message generation Browsing ◮ Host: domain name of host of resource (means relative Applications URLs can be used) HTTPS ◮ Accept-Charset, Accept-Encoding, Accept-Language: Certificates indicate the character sets, encodings and languages Summary that client can accept ◮ Authorization: include user credentials (e.g. username, password) if authorization is required ◮ User-Agent: indicates information about the client (user agent), e.g. web browser ◮ Referrer: URL from which this request came from ◮ Content-Encoding: encoding or compression, e.g. gzip ◮ Content-Length: length of message body on bytes ◮ Content-Type: the type of content in message body ◮ Last-Modified: indicates data/time when content was last modified on server 9/31
ITS335 Contents Web Security Browsing Web Browsing Applications HTTPS Certificates Web Applications Summary Confidential Web Communications with HTTPS Digital Certificates Summary 10/31
ITS335 Web Applications Web Security ◮ Plain, static web pages: HTML, images and other files Browsing served to browser Applications ◮ But many applications use dynamic content HTTPS ◮ Content server to browse changes depending on request Certificates ◮ Provides interactive, tailored content Summary ◮ Client-side: JavaScript, Flash, Silverlight, Java ◮ Server-side: CGI, ASP, PHP, Coldfusion, Java, . . . ◮ Content stored in databases 11/31
ITS335 Dynamic Content with Server-Side Processing Web Security Browsing Applications HTTPS Certificates Summary 12/31
ITS335 What are the security issues? Web Security ◮ Data transmitted between browser and server is Browsing confidential: encryption with HTTPS Applications ◮ Browser sure it is communicating with intended server: HTTPS digital certificates Certificates ◮ Server sure it is communicating with intended user: Summary password authentication, session management ◮ Actions performed by server (engine) are appropriate: authentication, access control ◮ Actions of user (of browser) are kept private: anonymity services 13/31
ITS335 Contents Web Security Browsing Web Browsing Applications HTTPS Certificates Web Applications Summary Confidential Web Communications with HTTPS Digital Certificates Summary 14/31
ITS335 HTTPS Web Security ◮ HTTPS: HTTP over SSL (or TLS) Browsing ◮ URL uses https:// Applications ◮ Web server listens on port 443 HTTPS Certificates ◮ Encrypt: URL of requested document, contents of Summary document, contents of browser forms, cookies, contents of HTTP header ◮ Server is authenticated using certificate (using SSL) ◮ Client is authenticated using password (using HTTP) 15/31
ITS335 SSL and TLS Web Security ◮ Secure Sockets Layer (SSL) originated in Netscape web Browsing browser Applications ◮ Transport Layer Security (TLS) standardised by IETF HTTPS ◮ SSLv3 and TLS are almost the same Certificates Summary ◮ SSL provides security services to application layer protocols using TCP ◮ SSL architecture consists of multiple protocols 16/31
ITS335 SSL Architecture Web Security Browsing Applications HTTPS Certificates Summary Record: provides confidentiality and message integrity Handshake: authenticate entities, negotiate parameter values Change Cipher: change cipher for use in connection Alert: alert peer entity of status/warning/error 17/31
ITS335 Connections and Sessions Web Security ◮ SSL connection corresponds with TCP connection Browsing ◮ Client and server may have multiple connections Applications ◮ SSL session is association between client and server HTTPS ◮ Session created with Handshake protocol Certificates ◮ Multiple connections can be associated with one session Summary ◮ Security parameters for session can be shared for connections ◮ State information is stored after Handshake protocol ◮ Session: ID, certificate, compression, cipher spec, master secret, . . . ◮ Connection: random values, encrypt keys, MAC secrets, IV, sequence numbers, . . . 18/31
ITS335 SSL Record Protocol Operation Web Security Browsing Applications HTTPS Certificates Summary 19/31
ITS335 SSL Handshake Protocol Web Security ◮ Allow client and server to authenticate each other Browsing ◮ Negotiate encryption and MAC algorithms, exchange Applications keys HTTPS ◮ Key Exchange: RSA, Diffie-Hellman Certificates ◮ MAC: HMAC using SHA or MD5 Summary ◮ Encryption: RC4, RC2, DES, 3DES, IDEA, AES ◮ Multiple phases: 1. Establish security capabilities: client proposes algorithms, server selects one 2. Server authentication and key exchange 3. Client authentication and key exchange 4. Finish setting up connection 20/31
ITS335 Contents Web Security Browsing Web Browsing Applications HTTPS Certificates Web Applications Summary Confidential Web Communications with HTTPS Digital Certificates Summary 21/31
ITS335 Authentication and Encryption in Web Browsing Web Security ◮ Browser and server do not have pre-shared secrets Browsing ◮ Use public key cryptography to securely exchange secret Applications key HTTPS ◮ RSA/DSA Certificates ◮ Diffie-Hellman key exchange Summary ◮ Elliptic curve cryptography ◮ Once a secret key is exchanged, use symmetric key encryption ◮ AES, RC4, 3DES, . . . ◮ E.g. with RSA: if a server sends browser its RSA public key, how does browser know it is indeed RSA public key of server? ◮ Get a trusted third party to confirm it is the servers RSA public key 22/31
ITS335 Digital Certificates Web Security Step 1: Server Obtains Digital Certificate Browsing Applications ◮ Server (owner) creates key pair: ( PU s , PR s ) HTTPS ◮ Server confirms identity, ID s , with trusted third party Certificates called Certificate Authority Summary ◮ CA issues server with a digital certificate by signing relevant info: C s = ( ID s || PU s || T , E ( PR CA , H ( ID s || PU s || T )) ◮ A timestamp, T , can be used to determine how long the certificate is valid ◮ X.509 specifies standard format of certificates 23/31
ITS335 Digital Certificates Web Security Step 2: Server Sends Digitial Certificate to Browser Browsing Applications ◮ When browser initiates communications with server, HTTPS server responds with C s Certificates ◮ Browser verifies signature using PU CA Summary ◮ Assumes browser already knows and trusts PU CA ◮ PU CA is stored in self-signed certificate: C CA = ( ID CA || PU CA || T , E ( PR CA , H ( ID CA || PU CA || T )) ◮ Once verified, browser can choose secret value and send it encrypted using PU s to server 24/31
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